This invention is directed to providing a combined air vent and overpressure relief valve assembly for installation in an opening in the upper end wall of a chamber which in use will be filled with liquid under pressure, such particularly as the interior of a submersible fuel pump of the type which is commonly located in the fuel tank of a motor vehicle.
A problem indigenous with submersible pumps is that some provision is needed for purging air from the interior of the pump, and also a provision for relieving pressure in the pump if, for example, the pump outlet or some point downstream therefrom should be partially or completely blocked. The first of these needs results from the fact that when air accumulates in a submersible pump of this type, the pump may be incapable of generating sufficient pressure to force the air out through the check valve which is normally present in the output line from the pump.
This initial need can be taken care of by a check valve operating in the reverse direction which will allow air to escape but will be closed by the hydraulic pressure as soon as the air has been evacuated. There still remains, however, the other problem of excess pressure, and this has been taken care of in the past by the provision of a third check valve which will open for release of liquid from the chamber in response to hydraulic pressure substantially higher than is needed to close the air vent valve.